.\" $OpenBSD: sem_post.3,v 1.5 2013/06/05 03:44:50 tedu Exp $
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.\" Copyright (C) 2000 Jason Evans <jasone@FreeBSD.org>.
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.\" $FreeBSD: src/lib/libc_r/man/sem_post.3,v 1.10 2001/10/01 16:09:09 ru Exp $
.Dd $Mdocdate: June 5 2013 $
.Dt SEM_POST 3
.Os
.Sh NAME
.Nm sem_post
.Nd increment (unlock) a semaphore
.Sh SYNOPSIS
.In semaphore.h
.Ft int
.Fn sem_post "sem_t *sem"
.Sh DESCRIPTION
The
.Fn sem_post
function increments (unlocks) the semaphore pointed to by
.Fa sem .
If there are threads blocked on the semaphore when
.Fn sem_post
is called, then the highest priority thread that has been blocked the longest on
the semaphore will be allowed to return from
.Fn sem_wait .
.Pp
.Fn sem_post
is signal-reentrant and may be called within signal handlers.
.Sh RETURN VALUES
.Rv -std sem_post
.Sh ERRORS
.Fn sem_post
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa sem
points to an invalid semaphore.
.El
.Sh SEE ALSO
.Xr sem_destroy 3 ,
.Xr sem_getvalue 3 ,
.Xr sem_init 3 ,
.Xr sem_open 3 ,
.Xr sem_wait 3
.Sh STANDARDS
.Fn sem_post
conforms to
.St -p1003.1-96 .
